1. Field of the Invention
The present invention relates to a fluid-filled vibration damping device in which damping effects are obtained based on the flowing action of a fluid sealed in the interior, and in particular relates to a fluid-filled vibration damping device which is suitable for use as automobile engine mounts or body mounts, differential mounts, and suspension bushes.
2. Description of the Related Art
JP-U-4-43636 discloses one type of known damping device used as a damping connector or damping support mounted between members forming a vibration transmission system. The disclosed damping device includes an inner shaft and outer cylinder disposed radially apart from each other, which are connected by a rubber elastic body, and is capable of exhibiting damping effects, based on the flowing action of a non-compressible fluid, against vibrations input in an axis-perpendicular direction. In this type of damping device, a pair of fluid chambers connected by an orifice passage are generally located facing on both sides, in the axis-perpendicular direction, of the inner shaft, so as to obtain damping effects based on the resonance action of the fluid flowing through the orifice passage when vibrations are input in the axis-perpendicular direction.
The damping effects of damping devices are sometimes needed for vibrations with several or a wide range of frequencies. For example, automobile damping devices are required to have excellent damping performance against vibrations with several or a wide range of frequencies, from the low frequency range to the high frequency range, because the input vibrations that need to be absorbed will vary depending on the vehicle traveling state.
However, a problem with the fluid-filled vibration damping device structured in the above manner is the narrow range of frequencies in which it is possible to effectively bring about damping effects on the basis of the resonance action of the fluid flowing through the orifice passage. It is thus difficult to obtain sufficient damping effects against vibrations with several or a wide range of frequencies, and difficult to realize the necessary damping properties. A major problem in particular is the dramatic loss of damping performance upon the development of extremely high dynamic spring associated with increased flow resistance in the orifice passage when the input vibrations are of a higher frequency range than the frequency range for which the orifice passage has been tuned.
To address this problem, as described in JP-A-10-331901, for example, it has been proposed that an actuator should be incorporated to control the switchover between a plurality of fluid passages, so as to deliberately switch between damping effects according to the input vibrations. However, problems with this damping device are that the incorporation of the actuator results in an extremely complex structure which is difficult to manufacture, as well as in higher costs and larger sizes.
In another proposal, as described in JP-A-7-127684, for example, a barrier wall component formed by a rubber elastic body, dividing a pair of fluid chambers formed on both sides of an inner shaft, is made in the form of a readily deformable thin-walled component, and pressure fluctuations prompted in one fluid chamber during the input of vibrations in the high frequency range escape into the other fluid chamber due to the elastic deformation of the thin-walled component, thereby preventing the development of extremely high dynamic spring.
However, because the thin-walled component is formed by the rubber elastic body itself elastically connecting the inner shaft and outer cylinder in this damping device, providing the thin-walled component runs the risk of adversely affecting the spring properties of the damping device. Furthermore, because the thin-walled component is formed by the rubber elastic body itself elastically connecting the inner shaft and outer cylinder, input vibrations directly cause elastic deformation of the thin-walled component. It is thus difficult to make the thin-walled component thin enough when attempting to realize the spring properties required of the damping device and ensure the durability of the thin-walled component. It is therefore sometimes difficult to effectively obtain low dynamic spring effects based on pressure fluctuation absorbing action with this type of thin-walled component.